1. Field of the Invention
The present invention relates to a face authentication system and a face authentication method for performing a registration process and a verification process of authentication data based on three-dimensional data on a face area of a human.
2. Description of Related Art
Conventionally, there have been proposed various biometric methods, using two-dimensional image data on a face area of a human. For instance, there is known a biometric method comprising: acquiring a two-dimensional image including a face area of a person (hereinafter, also called as “subject”) whose authentication is required; preregistering image information after specifying the face area by matching the acquired two-dimensional image with a predetermined face template; and comparing an image on the face area acquired in authentication with the registered image in feature quantity.
There is also proposed a biometric method for acquiring three-dimensional data on a face area in addition to two-dimensional image data, and performing personal authentication by referring to the two-dimensional image data and the three-dimensional data (see e.g. Japanese Unexamined Patent Publication No. 2003-162730). With use of the method, an authentication process can be performed in a state that the three-dimensional feature quantity on the face area is included. This enables to realize more accurate and efficient authentication. Generally, a non-contact optical three-dimensional shape measuring device is used to obtain three-dimensional data on the face area.
In optically acquiring three-dimensional data on a face area of a subject, it is highly likely that a part of the three-dimensional data may be missing depending on a face condition of the subject or a like factor. For instance, in the case where the subject wears eyeglasses, specular reflection may occur on the eye portions of the subject, which leads to a failure of receiving reflection light suitable for measurement. In a face area where the subject wears a moustache/beard, light scatters on the moustache/beard area because of a complicated surface configuration of the moustache/beard area. This may also lead to a failure of receiving reflection light suitable for measurement. In such a case, the quality of three-dimensional data may be degraded, with the result that authentication precision may be lowered. Also, a relatively long time is required to acquire three-dimensional data. The face of the subject may move during the data acquisition. This may also degrade the quality of three-dimensional data.
In view of the above, it is desirable to rate the quality of three-dimensional data acquired at the time of registering authentication data. The same idea is also applied to three-dimensional data to be acquired in verification. Heretofore, there has not been proposed a method for accurately rating the quality of three-dimensional data. For instance, the above publication discloses an approach of using eyeglasses or a moustache/beard as a targeted object for analysis in authentication. However, the publication merely discloses use of eyeglasses or a moustache/beard as a feature quantity, and does not disclose rating the quality of three-dimensional data.